A traveler's tale

Pytheas of Massalia was a Greek polymath who was born in what is now Marseilles, France in around 350 B.C.E., making him a generation younger than Aristotle, and an almost exact contemporary of Alexander the Great.  When I tell you about what this guy did, you will (I hope) be shocked that his name isn't as familiar to students of history as the other two gentlemen I mentioned.

The reason for his relative obscurity is one that is all too common; he is known to have written a single book, Τὰ Περὶ τοῦ Ὠκεανοῦ (On the Ocean), possibly supplemented by a second work, Περίοδος Γῆς (Around the Earth), although some scholars believe those were two alternate titles for the same account.  In any case, nothing of his writing survives except for excerpts and references to him and his accomplishments in other writing, most notably in the books of such luminaries as Strabo and Pliny the Elder.  Sadly, like so much of the brilliant work of antiquity, all the copies of Pytheas's book (or books) have fallen prey to the ravages of time.

What Pytheas of Massalia recorded in his writings would have been an incredible feat for anyone, and nearly beggars belief for someone in the fourth century B.C.E.  He'd heard that there were these islands off the northwest coast of Gaul, inhabited by some curious folks called the Celts, and he decided to go see for himself.

How he started his travels is uncertain.  At this point in history, the Carthaginians had control of the Straits of Gibraltar, and the hostilities between them and damn near everyone else in the region would have made passage a dicey affair.  There's a possibility that he crossed Gaul overland and launched from the mouth of either the Garonne or Loire River into the Bay of Biscay.  In any case, once he got into the Atlantic, it was off to the races.

He sailed up the west coast of England, stopping to do considerable travel on foot, up through the Irish Sea, past the Isle of Man and the Hebrides.  He is the first to note that the natives called the main island Prydain -- Romanized to Britannia -- which is where we get the modern name Britain.

Then, amazingly, Pytheas kept going.

Marble sculpture of Pytheas by Auguste Ottin (1860)  [Image licensed under the Creative Commons Rvalette, Pythéas, CC BY-SA 3.0]

There are credible claims that he made it as far as either Iceland or the Lofoten Islands -- which it was is uncertain.  He reports being in a place "six days north of Britain," an island of "perpetual frost and snow" where, nevertheless, "the Sun never sets" -- the first known Greek to realize what happens to day length when you're above the Arctic Circle.  Not content even yet, he began to head east, making his way into the Baltic Sea.  There, he met a people he called the Gutones (almost certainly the Goths), who made their living trading amber, which is abundant in what is now Poland, Lithuania, and Latvia.  From there he went inland, possibly traveling along the region's many navigable rivers.  It's thought that he made it all the way to what was then called Scythia, along the north shore of the Black Sea.

One of the most remarkable things about Pytheas and the others who traveled with him is how well received they were.  Despite the reputation for hostility that the ancient Celts, Norse, Teutons, Baltics, and Scythians all had, there's no indication Pytheas ever had any trouble -- just showing that for the most part, if you treat people with kindness and respect, they reciprocate.  Even the "barbarians."

Pytheas also had a couple of striking scientific achievements -- using the changing elevation above the horizon of familiar stars as he went north, he tried to estimate the circumference of the Earth using a sextant.  His measurements were off -- Eratosthenes of Cyrene did way better a hundred years later -- but still, it was a creditable attempt.  Second, he is the first person known to have associated the tides with the position and phases of the Moon, a remarkable idea during a time when the celestial objects were supposed to be gods of various sorts, and there was no inkling of a law of gravitation.

Finally, Pytheas made his way back home to write his book(s), and lived the rest of his life in comfort in his villa in Massalia.  But can you imagine what he must have seen and experienced?  Meeting the people of the British Isles, Scandinavia, Germany, the Baltic lands, and Scythia before they'd had much chance to contact people from other cultures.  Seeing the enormous expanse of the oceans and the pack ice of the Arctic from the deck of a simple sailing ship.  What an adventure -- and what extraordinary curiosity, drive, and courage.

It's such a tragedy that Pytheas's original manuscript(s) have been lost; imagine what more we could learn from his voyages by reading a first-hand account.  Regardless, he was an extraordinary person, someone determined to see as much of the world as he could, and who amazingly (considering the times) lived to tell his traveler's tale to the astonishment of his friends back home.

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Miraculous mathematics

I've blogged before about "miraculous thinking" -- the idea that an unlikely occurrence somehow has to be a miracle simply based on its improbability.  But yesterday I ran into a post on the wonderful site RationalWiki that showed, mathematically, why this is a silly stance.

Called "Littlewood's Law of Miracles," after British mathematician John Edensor Littlewood, the man who first codified it in this way, it goes something like this:

• Let's say that a "miracle" is defined as something that has a likelihood of occurring of one in a million.
• We are awake, aware, and engaged on the average about eight hours a day.
• An event of some kind occurs about once a second.  During the eight hours we are awake, aware, and engaged, this works out to 28,800 events per day, or just shy of a million events in an average month.  (864,000, to be precise.)
• The likelihood of observing a one-in-a-million event in a given month is therefore 1-(999,999/1,000,000)^1,000,000, or about 0.632.  In other words, we have better than 50/50 odds of observing a miracle next month!

Of course, this is some fairly goofy math, and makes some silly assumptions (one discrete event every second, for example, seems like a lot).  But Littlewood does make a wonderful point; given that we're only defining post hoc the unlikeliness of an event that has already occurred, we can declare anything we want to be a miracle just based on how surprised we are that it happened.  And, after all, if you want to throw statistics around, the likelihood of any event happening that has already happened is 100%.

So, like the Hallmark cards say, Miracles Do Happen. In fact, they're pretty much unavoidable.

Peter Paul Rubens, The Miracle of St. Ignatius (1617) [Image is in the Public Domain]

You hear this sort of thing all the time, though, don't you?  A quick perusal of sites like Miracle Stories will give you dozens of examples of people who survived automobile accidents without a scratch, made recoveries from life-threatening conditions, were just "in the right place at the right time," and so on.  And it's natural to sit up and take notice when these things happen; this is a built-in perceptual error called dart-thrower's bias.  This fallacy is named after a thought experiment of being in a pub while there's a darts game going on across the room, and simply asking the question: when do you notice the game?  When there's a bullseye, of course.  The rest is just background noise.  And when you think about it, it's very reasonable that we have this bias.  After all, what has the greater evolutionary cost -- noticing the outliers when they're irrelevant, or not noticing the outliers when they are relevant?  It's relatively obvious that if the unusual occurrence is a rustle in the grass, it's far better to pay attention to it when it's the wind than not to pay attention to it when it's a lion.

And of course, on the Miracle Stories webpage, no mention is made of all of the thousands of people who didn't seem to merit a miracle, and who died in the car crash, didn't recover from the illness, or were in the wrong place at the wrong time.  That sort of thing just forms the unfortunate and tragic background noise to our existence -- and it is inevitable that it doesn't register with us in the same way.

So, we should expect miracles, and we are hardwired to pay more attention to them than we do to the 999,999 other run-of-the-mill occurrences that happen in a month.  How do we escape from this perceptual error, then?

Well, the simple answer is that in some senses, we can't.  It's understandable to be surprised by an anomalous event or a seemingly unusual pattern.  Think, for example, how astonished you'd be if you flipped a coin and got ten heads in a row.  You'd probably think, "Wow, what's the likelihood?" -- but any other ordered pattern of heads and tails, say, H-T-T-H-H-H-T-H-T-T -- has exactly the same probability of occurring.  It's just that the first one looks like a meaningful pattern, and the second one doesn't. 

The solution, of course, is the same as the solution for just about everything; don't turn off your brain.  It's okay to think, at first, "That was absolutely amazing!  How can that be?", as long as afterwards we think, "Well, there are thousands of events going on around me right now that are of equally low probability, so honestly, it's not so weird after all."

All of this, by the way, is not meant to diminish your wonder at the complexity of the universe, just to direct that wonder at the right thing.  The universe is beautiful, mysterious, and awe-inspiring.  It is also, fortunately, understandable when viewed through the lens of science.  And I think that's pretty cool -- even if no miracles occur today.

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The outrage machine

As of this morning, I have now seen the following post five times:

It seems like it should be obvious this can't be true, because if there was a rule banning the posting the Lord's Prayer on Facebook, this post and the hundreds of others like it would have been deleted, which they weren't.  Apparently, that line of reasoning doesn't seem to occur to people, because instead, the whole thing elicited a chorus of "Amens" and lots of middle fingers raised by the members of the Religious Outrage Machine toward everyone they think is oppressing them, which is pretty much... everyone.

It's so widespread it made it to Snopes, which (of course) found there's no truth to it at all.  There is no prohibition against posting religious material on Facebook, as long as it doesn't involve hate speech.

So let's get something straight, okay?  You Christians in the United States are not a persecuted minority.  Estimates from polls in 2021 show that about 63% of Americans identify as Christian.  There is no basis whatever for the claims made in sites like TruthOnlyBible, which stated that there's a push toward conservative Christians being "[excluded] from basic services, such as air travel, hotel, cell phone, banking, internet shopping, and even insurance."

Seriously, considering how loud the conservative Christians are about airing their grievances at every possible opportunity, how long do you think an airline would last if they said "I'm sorry, you can't purchase a flight to Cancun with us because you're a Christian"?

The most bizarre thing about this claim is that in a lot of the United States, the opposite trend is true.  Despite the "no religious test" clause in the Constitution, in many parts of America it'd be flat-out impossible to get elected if you're not a Christian (and in some of those places, you have to be a particular sort of Christian).

Hell, the second in line for the presidency is an ultra-conservative, anti-LGBTQ, fundamentalist young-earth creationist.

Remind me again how embattled y'all are?

The fact is, no one is trying to stop people from praying, posting Christian stuff online, wishing people Merry Christmas, or going to church.  No one.  You're just as free to be religious as you ever were.  Maybe more people these days are willing to say, "You can't force your religion on me," but that does not equate to "And I'd like to force my lack of religion on you."

But people aren't galvanized by messages like "we're all just trying to get along, here."  Despite my frequent bafflement at why people seem to enjoy feeling indignant, I have to admit that feeding the outrage machine works.  It's why the imaginary "War on Christmas" absolutely refuses to die.  You'd think that twenty years would be enough to convince everyone that no one, not even an Evil Atheist like myself, is trying to kill Christmas, but another thing that comes along with this mindset appears to be a complete resistance to facts and logic.

If you convince people they have something to be scared and mad about, they act.  Which is why fear-mongering is all over the news.  It's why politicians are experts in stoking anger.

"Vote for me, I'll fix what I just made you afraid of" is a mighty powerful message.

But as far as Facebook and prayers -- as I've said more than once here at Skeptophilia, if you're trying to persuade someone of something, blatantly lying about it does not make your case stronger.  And while it might be easy to take advantage of people who can't be bothered even to do a thirty-second Google fact-check search, ultimately what it does is blow your own credibility to smithereens.

So please, please stop reposting bullshit like this.  Can I get an amen to that?

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Passing shadow

In astronomy, an occultation occurs when one celestial object passes in front of another, temporarily blocking it from sight (from the perspective of an observer on Earth).  Some occultations are entirely unremarkable; the Moon occults thousands of stars every month on its trips around the Earth, and we barely notice it because it's so ordinary.  And technically, solar eclipses are occultations, even though we don't usually think of them that way.

Other occultations, though, are rarer and more interesting.  The rings of Uranus were discovered in 1977 when they occulted the star SAO 158687, making it appear to blink on and off five times.  Pluto occulted stars in 1988, 2002, and 2006, and as it passed in front of the stars the alteration in the stars' light allowed astronomers here on Earth to study the chemistry of Pluto's thin atmosphere, a technique called atmospheric limb sounding.

Of course, because the two objects have to be lined up perfectly, occultations of bright and/or familiar objects are rare occurrences.  Jupiter, for example, is going to occult the planet Saturn -- but not until February 10, 7541.

That's a long time to wait.

Because natural occultations are so uncommon, there's a proposal to create an artificial version of occultation -- and use it to try and find more exoplanets.  A proposed orbiting telescope called BOSS (for Big Occulting Steerable Satellite -- of course it has a cute acronym, because these are astronomers we're talking about) will, if deployed, have a shield that can block the light of stars and allow the much dimmer reflected light of their planets to be detected.  Ordinarily, the glare of even an ordinary star is so bright that it swallows up the signal; shielding it, creating an artificial eclipse, might reveal hidden planetary systems.

The reason this topic comes up is that a loyal reader of Skeptophilia alerted me to an occultation that is going to occur at 1:08 AM, Greenwich Mean Time, tonight.  The bright star Betelgeuse is, for seven minutes, going to be covered by the asteroid 319 Leona -- so for that time, the familiar figure of Orion will appear to be missing his left shoulder.

Unfortunately for me, the occultation won't be visible from upstate New York, but you're in luck if you're in the southern Mediterranean or the southern tip of Florida.  Here's a map of where the occultation will be visible:

The coolest part is that Betelgeuse is so huge -- if it were where the Sun is, its outer edge would be near the orbit of Jupiter, and we'd be inside the star -- that despite its distance of 548 light years, its angular diameter is larger than that of the much closer asteroid that's occulting it.  So through a telescope, it'll be an annular occultation -- the occulting object won't quite be able to cover the entire star up.

Even so, Betelgeuse will for seven minutes dim to near invisibility to the naked eye.

You have to wonder what the ancients would have made of this.  Many cultures believed the heavens to be timeless and changeless, which is why the appearance of comets and events like the supernovae of 1054 and 1604 ("Kepler's supernova") were considered such portents of evil.

Even though we now know better, it still will be a little unnerving to have such a familiar star suddenly appear to vanish from sight.  It's a pity I won't get to see it -- it's a little late to purchase a plane ticket for Spain.  If the path of occultation passed across upstate New York, I'd even get up in the middle of a frigid December night to see one of the brightest stars in the night sky blink off for a few minutes.

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The honey hunters

One of the things I learned from 32 years of teaching biology is that many non-human animals are way smarter than we give them credit for -- and its corollary, which is that we humans are not as far separated from the rest of the natural world as many of us would like to think.

A charming piece of research in Science this week illustrates this point brilliantly.  It's about a species of African bird, the Greater Honeyguide (its scientific name, which I swear I'm not making up, is Indicator indicator).  It's found in open woodland in most of sub-Saharan Africa, and has a very specialized diet -- it lives on bee eggs, larvae, and wax (it's one of the few known animals that can digest wax).

Illustration of a Greater Honeyguide by Nicolas Huet (1838) [Image is in the Public Domain]

Because of its diet, local residents have developed a mutualistic relationship with honeyguides, a relationship that is what gives the birds their common name.  People living in the region listen for the bird's call and then follow it to find the bees' nests it was attracted to.  The people tear open the nests and take the honey -- and the bird gets the larvae and the wax.  Many cultures that live in the honeyguides' range have developed specific calls to attract the birds when they're ready to go on a honey hunt.

The study, led by ecologist Claire Spottiswoode of the University of Cambridge, looked at the fact that honeyguides seem to learn the specific calls used by the people they live near.  Initially, it was uncertain if the people had figured out what the birds responded to, or if the reverse was true and the birds had learned what noises the people made.  So she and her team decided to test it; they used recordings of individuals from two cultures that are known to use honeyguides, the Hadza of Tanzania and the Yao of Malawi and Mozambique.  The Hadza employ a complex series of whistles to summon their helpers, while the Yao make a "brrr-huh" sound.

Both signals work just fine, but only in particular regions.  When a recording of the Hadza signal is played in Malawi, or a recording of the Yao signal is played in Tanzania, the birds don't respond.  The birds have evidently learned to recognize the specific calls of their partners in the region where they live -- and don't "speak the language" used elsewhere.

Spottiswoode's team also found there are two places where the symbiotic relationship is falling apart.  In more urban areas, where commercial sugar is widely available, there are fewer people engaged in honey hunting, so the birds have decided they're better off working as free agents.  Even more interesting, in some areas in Mozambique, the Yao discovered that if they destroy the wax and the rest of the hive, the honeyguides will stay hungry and look for other nests.  But... the birds are learning that their human partners are stiffing them, and they're becoming less likely to respond when called, so the human honey hunters are having less overall success.

So even birds can recognize when they're getting a raw deal, and put a stop to it.

The more we find out about the other life forms with which we share the planet, the more commonality we find.  Everything in the natural world exists on a continuum, from our physiology and our genetics to characteristics many thought of as solely human traits, like emotion, empathy, and intelligence.

So be careful when you throw around terms like "bird-brain" -- they're not as far off from us as you might like to believe.

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Geological toothpaste

One of the fun things about science is that sometimes, when you look closely at a phenomenon, you find out that what you thought was fairly simple turns out to be not only complex but just flat-out weird.  That was my reaction to something I first heard about only a couple of days ago, which (like the topic of yesterday's post) comes from the realm of geology.

Continental slopes are generally pretty straightforward.  They represent a sharp boundary between continental crust (usually thick, cold, and relatively old) and oceanic crust (by contrast, thin, hot, and fairly recent).  The slopes are steep dropoffs -- the topography of the ocean floor is no gradual decline down toward the abyss -- and the continental shelves, the shallow regions of varying widths that ring the continents, are actually geologically part of the continent.  (They just happen to be covered by sea water.)

So the continental slopes shouldn't be that complicated.  They're a narrow transitional band separating shallow regions connected to the continental land masses from the very different geological realm of the deep ocean.

But then there's the Sigsbee Escarpment.

The Sigsbee Escarpment is a stretch of the continental slope in the Gulf of Mexico, south of coastal Louisiana, Mississippi, Alabama, and Florida.  The first clue that there was something weird going on there is that the continental shelf north of it is a good bit wider than it should be -- certainly wider than a lot of continental shelf regions.  This is great for the fishing industry, which thrives in shallow continental shelf regions.  The deep ocean has far less in the way of life, largely due to the fact that the depth makes significant vertical mixing difficult, so nutrients that settle to the ocean floor tend to stay there.  Any given cubic meter of surface water over the deep ocean is unlikely to have much living in it beyond single-celled organisms.

Most continental shelves are relatively narrow, but the Sigsbee Escarpment sticks way out into the Gulf, and the reason why has to do with the combination of something that happened 150 million years ago and something that happened two thousand kilometers away.

[Image courtesy of Harry H. Roberts and the National Oceanic and Atmospheric Administration]

At the beginning of the Jurassic Period, around two hundred million years ago, North and South America were joined (well, everything had been joined not long before; Pangaea had lasted through most of the Triassic Period).  Rifting opened up what would eventually become the Gulf of Mexico, letting seawater into a new embayment that initially was quite shallow.  The climate was generally hot, so for the next fifty million years, the evaporation rate was high, and this water became extremely saline, leading to the deposition of huge quantities of crystalline salt on the seafloor.

These salt deposits are found all over the southeastern United States, and what are responsible for the Lake Peigneur disaster in November of 1980.  Lake Peigneur is a broad, brackish lake near Delcambre in Iberia Parish, Louisiana, which unfortunately is right above a huge salt deposit that had been mined for years by the Diamond Crystal Salt Company.  The problem is, the area is also a prime spot for oil drilling -- oil deposits and salt domes are frequently found in the same geological context -- and a Texaco oil rig drilling in the lake floor accidentally punched through into a cavern that had been excavated by the Salt Company.  Suddenly the bottom of the lake collapsed, creating a vortex like water going down a bathtub drain as the entire lake drained into the cavern.  The sinkhole swallowed the oil rig, eleven barges, a tugboat, hundreds of trees, and 26 hectares of land from the lake edge.  Where the lake had been, all that was left was an expanse of salty mud.

But back to the Sigsbee Escarpment.  The salient point here is that this same salt deposit, created during the Jurassic Period, extends offshore.  And that's where the second factor comes in.

The Laramide Orogeny is a complex series of events that is mostly responsible for raising the Rocky Mountains.  What had been relatively flat terrain, from Arizona up to Alberta, was now rapidly increasing in elevation and steepness.  Well, there's a general rule in geology that if you increase the angle at which a land surface sits, you increase the rate of erosion from running water; rivers run faster, can carry more suspended debris, and have a greater capacity for abrasion.  The raising of the Rocky Mountains meant that as they were lifted, the forces of erosion started tearing them down -- and all of that pulverized rock had to go somewhere.

Ultimately, any of it east of the Continental Divide ended up in the tributaries to the Mississippi River, and was flushed out into the Gulf of Mexico.

This plume of debris -- some of it from thousands of kilometers away -- settled out over the Jurassic salt deposits, and the weight of it started exerting significant downward pressure.  And salt -- especially the saturated salt mush that was at the bottom of the sea -- flows when it's compressed.  So like toothpaste squeezed from the world's largest tube, the salt domes squished outward, forming the lobes that are on the southern edge of the Sigsbee Escarpment.

Geologist Harry H. Roberts, of Louisiana State University, writes, "This process continues today.  As sediments have been continually added to the northern and northwestern Gulf rim, salt has been squeezed seaward in front of a constantly thickening wedge of sediment.  Today, the steep transition between the bottom of the continental slope and the deep Gulf floor, called the Sigsbee Escarpment, represents the old Jurassic Louann salt formation being squeezed seaward over much younger sediments."

So what started out seeming simple -- the steep boundary between continental shelf and deep ocean -- turns out not to be that simple after all, and way more interesting.

But that's how science is, isn't it?  Answering one question raises a hundred more, but that's the thrill of it.  As physicist Brian Greene put it, "Science is a way of life.  Science is a perspective.  Science is the process that takes us from confusion to understanding in a manner that's precise, predictive and reliable -- a transformation, for those lucky enough to experience it, that is empowering and emotional."

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The story of the bands

Something that strikes me about many scientific discoveries is how they so often come from someone noticing something the rest of us had overlooked or thought insignificant -- and afterward, most importantly, the person asking, "Why?"

A now-familiar example of this is the discovery by the father-and-son team of Luis and Walter Alvarez of the thin iridium-bearing clay layer at the boundary between Cretaceous rocks and Paleocene rocks -- analysis of which led to the discovery of the dinosaur-killing Chicxulub Meteorite Impact.  Without their questioning why there was a narrow layer of heavy-metal-enriched clay at the boundary, everywhere on Earth where there are rocks of that age, we might never have found out about one of the major events in the history of life on Earth.

Another example, less well known, has to do with the banded iron formations found in locations all over the world, including Australia, Brazil, Canada, India, Russia, South Africa, Ukraine, and the United States.  They're striking in appearance, sometimes hundreds of meters thick, with alternating layers of light-colored iron-poor and dark, reddish-brown iron-rich chert or limestone.  Here's an example from near Fortescue Falls in Western Australia:

[Image licensed under the Creative Commons Graeme Churchard from Bristol, UK, Banded iron formation Dales Gorge, CC BY 2.0]

Most of us, I think, would say "pretty rock formation" and leave it at that; a smaller number would recognize the fact that they were sedimentary, and wonder why the colors alternate.  Geologist Preston Cloud, though, took it several large steps farther -- and what he came up with is a little mind-blowing.

What first struck Cloud as curious about banded iron formations is that they're all about the same age.  Regardless of whether they're in Australia or Ontario, just about every banded iron formation studied was deposited around 2.4 billion years ago.  But what could create this pattern not just in one location, but in widely-scattered spots all over the planet?  Whatever the process was must have happened everywhere simultaneously -- and rapidly.

Cloud's hypothesis, which is now well-accepted, is that banded iron formations represent the fingerprint of something called the Great Oxidation Event.  Here's basically what we think happened.

Early living things were largely scavengers, living from abiotically-produced organic compounds dissolved in seawater (and the decomposing bits of dead cells).  These compounds were abundant -- an anoxic atmosphere, rich in reducing compounds like ammonia, methane, and carbon monoxide, together with an energy source like ultraviolet light, generates organic compounds of all sorts.  (As the Miller-Urey experiment conclusively demonstrated.)

But there's always competition between species, and sometimes mutations can create proteins or structures that allow organisms to able to access resources faster or more efficiently than their neighbors.  And that's what happened when a single-celled bacteria evolved a gene to produce chlorophyll, which can quickly capture energy from visible light and store it as chemical energy.

In other words: photosynthesis.

This had only one downside, but it was a huge one.  Photosynthesis generates molecular oxygen.  Oxygen is highly reactive, a strong oxidizer (thus the name), and tears apart organic compounds as quickly as they form.  The presence of oxygen, first dissolved in seawater and then liberated into the atmosphere, did three things.

First, it shut off the abiotic production of excess organic compounds, eliminating the food source for most of life on Earth.

Second, it was directly toxic to most cells, except for the (very) few which had detoxifying enzymes like superoxide dismutase to cope with living in an oxygenated environment -- or which were capable of metabolizing it, using a pathway we now call aerobic respiration and which we have become completely dependent upon.  (It's amazing to think about, but our energy-production system originally evolved as a way to mitigate the poisonous effects of molecular oxygen.)

Third, the oxygen reacted with dissolved ferrous (II) ions in seawater, and altered them to mostly-insoluble ferric (III) ions, which settled out on the ocean floor.  This process, however, bound up the available oxygen, so the reaction dropped oxygen levels, and for a while any iron eroded into the oceans was dissolved as ferrous ions again.  But eventually the photosynthesizing bacteria pumped out enough oxygen that the iron precipitated once more.  The result: alternating layers of iron-poor chert when the oxygen levels were low, and iron-rich chert when the oxygen levels rose.

Eventually, of course, the oxygen rose and stayed high.  By this time, damn near all life on Earth had died; the only ones left were anaerobes that could hide (like the bacteria we still have in deep-sea mud and other anaerobic habitats), and aerobes like our own ancestors that had metabolic pathways to cope with the presence of oxygen.

And the alternating pattern of light and dark layers in banded iron formations chronicle the rising and falling of oxygen during one of the pivotal moments of Earth's prehistory.

Certainly a large part of being a successful scientist is intensive training in a specific field, but I think sometimes there's not enough attention given to another facet of it -- the role of creativity.  The scientists who make important discoveries are usually the ones who notice things the rest of us might just walk past, wonder about them, and most importantly, draw connections between disparate realms to find answers (in this case, geology, chemistry, and biology).  Without this combination of technical knowledge, curiosity, and insight, we would know far less about the universe we live in -- and what an impoverished understanding we would be left with.

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